'No' campaign launches in Sydney

Meanwhile, Senator Corey Bernardi spearheaded the anti same-sex marriage campaign's national launch in Sydney on Saturday night, joined by prominent coalition politicians Matt Canavan and Concetta Fierravanti-Wells, who all took to the podium under blue and pink lights to champion the no vote.

An estimated 1000 people, many with shirts and placards bearing the slogan "It's ok to say 'no'", filled the International Conference Centre at Darling Harbour.

Senator Bernardi, who received a standing ovation, warned the audience of "weaponised" anti-discrimination laws and "legal warfare" against supporters of traditional marriage if the Marriage Act is changed to include same-sex couples.

Free speech was under attack from those seeking to redefine marriage, and their mission would have predictable consequences, he added.

"We're under assault because we're on the right side of legal and moral history," he said.